"What more suitable place for a green roof than the headquarters of America's conservation department in Washington, DC?" Secretary Kempthorne asked.

"With more than half of Washington, DC covered with paved or constructed surfaces that do not allow water to infiltrate the ground, 75 percent of rainfall becomes runoff," he said. The vegetation and soil on the green roof will absorb rainwater and curb runoff.

Washington, DC has a enormous problem from stormwater runoff and sewer overflows. Each year, at least a billion gallons of raw sewage are discharged into the Potomac River, Anacostia River and Rock Creek - all tributaries of the fragile Chesapeake Bay watershed.

The green roof on the Main Interior Building will help ease this problem by holding up to seven-tenths of an inch of rainfall to reduce stormwater runoff entering the sewage system.

The green roof also will improve water quality by neutralizing the effects of acid rain and filtering pollution from rain and snow. And it provides habitat for songbirds and pollinators.

The plants will shield the roof from the Sun's direct rays, which extends the roof's life span, insulates the building during the summer and saves energy as well as mitigates urban heat island effects.

Inside the building, it will reduce noise transfer from the outdoors and provide a visually attractive sight for employees and visitors.

Finally, the green roof is expected to improve the city's air quality a little by filtering the air that moves across the plants and, through photosynthesis, convert carbon dioxide into oxygen.

The green roof project started more than seven years ago when Mike Cyr, the National Business Center's chief of the Division of Facilities Management Services, read an article on the benefits of green roofs in Europe. Although green roofs were not commonplace at the time, Cyr decided to explore the possibility of installing a green roof on the Main Interior Building.

National Business Center personnel worked with in-house technical experts in the Office of Environmental Policy and Compliance. The group started by applying for and receiving free technical assistance from the Department of Energy's Federal Energy Management Program via the National Renewable Energy Laboratory.

The feasibility study confirmed a green roof would work on the Main Interior Building within specified limitations.

They also partnered with the U.S. Environmental Protection Agency and the General Services Administration to work through the contracting process to find a green roofing company. The roof was installed by Roofscapes, Inc. of Phildelphia, the award-winning company that installed the famous green roof on Chicago City Hall.

Deputy Secretary of the Interior Lynn Scarlett, Office of Environmental Policy and Compliance Director Willie Taylor, National Business Center Director Douglas Bourgeois and Cyr joined the secretary at the ribbon cutting ceremony on the roof terrace outside the South Penthouse.

At the ceremony, Kempthorne credited the deputy secretary for providing leadership on the green roof project.

"As the nation's premier conservation agency, Interior is pioneering use of green roofs at our historic headquarters in Washington. We want to apply a green thumb to our rooftops to reduce stormwater runoff," said Scarlett.

"Perhaps," she said, "we are entering what might be called the Age of Biology - the age of borrowing from nature's lessons as we manage lands, waters, and even our buildings."

The green roof is part of an ongoing modernization of the Main Interior Building will be conducted in six phases. Each phase will correspond to one of the six wings of the building, with a scheduled completion date of 2011 at an estimated cost of $175 million.